The invention relates to a spring brake cylinder, particularly for rail vehicles, having an emergency release device and having a spring piston which can be moved axially within a housing. On the one hand, the spring bake cylinder can be moved by means of an accumulator-type spring for operating the brake in the event of a pressure drop and, on the other hand, can be moved by a spring pressure chamber. The spring pressure chamber can be acted upon by a pressure medium, for releasing the spring brake, and has a normally locked, not self-locking threaded screw drive which is arranged in a flux or transmission of force between the spring piston and an output-side piston rod. The screw drive can be manually unlocked by way of a latch assigned to the emergency release device, in order to be able to release the spring brake without any pressure medium.
As a safety-relevant subassembly, spring brake cylinders of the above-described type are preferably used in rail vehicle construction for ensuring a brake operation when there is no brake pressure. In the case of a spring brake cylinder, the brake can be operated only by way of accumulator-type springs so that the spring brake cylinder can be used as a parking brake of a rail vehicle in the parked condition and as a safety brake when the compressed-air system is leaking or has failed during the driving operation.
A spring brake cylinder of the above-mentioned type is known from German Patent Document DE-OS 26 08 502. That spring brake cylinder consists essentially of a cylindrical housing with an interior accumulator-type spring which, for the brake operation, in the event of a pressure falling in the pressure chamber, acts upon the piston from the opposite side, so that the output-side piston rod moves out. A releasing of the brake takes place by the admission of pressure medium to the pressure chamber, in which case the accumulator-type spring is tensioned again and the piston rod moves in.
Furthermore, the spring brake cylinder has an emergency release device for the interruption of and the automatic returning into the above-explained normal operating mode of the spring brake cylinder, for the purpose of which a lockable, not self-locking threaded screw drive is arranged in the flux or transmission of force between the piston and the piston rod. The threaded screw drive consists essentially of a part which is rotatable with respect to the housing and of a part which is non-rotatable. The rotatable part may either be a nut which interacts with the piston and which is in a threaded engagement with a screw constructed on the piston rod; or, the rotatable part may be the screw which will then be rotatably disposed with respect to the piston rod, in which case its assigned nut is non-rotatably arranged with respect to the piston. Both carry out the same function.
During the normal braking operationxe2x80x94that is, when pressure is presentxe2x80x94, the rotatable part of the threaded spindle drive is locked by way of a latch, so that a rigid flux or transmission of force is established between the piston and the piston rod in order to permit a pressure-medium-operated restoring of the piston while tensioning the accumulator-type spring in the above-described manner. The emergency release device is required for releasing the brake in the event that no pressure is available for the compression of the accumulator-type spring. That is in an instance when the rail vehicle has to be movedxe2x80x94for example, during a switching. In this case, the transmission of force from the piston to the piston rod is manually interrupted from the outside by the unlocking of the not self-locking threaded screw drive by way of the latch, whereby a release of the brakes can take place without any pressure. The return into the original operating condition of the spring brake cylinder takes place automatically when pressure is available again which then, as a result of the compression of the accumulator-type spring, causes a return movement of the parts of the emergency release device.
In the prior art, this function is implemented by way of a detent pawl toothing provided at the outer radius on the rotatable part of the threaded screw drive, which detent pawl toothing meshes with the latch in the manner of a ratchet and pawl. The detent pawl toothing permits a relative rotating movement of the rotatable part of the threaded screw drive in only one direction, whereas the rotation into the other direction is prevented by the detent flanks of the toothing.
Here, the problem arises that, if the latching engages before the stoppage of the rotating parts, particularly, during a brief operation as the result of a slipping off the handle of the latch, the ratchet and pawl may be considerably worn and damaged. At extremely low temperatures, particularly as a result of the then reduced viscosity of the lubricant, the end position in the emergency-released condition may not be reliably reached so that the brake is not or cannot be completely released. This unfavorable condition will then be fixed by a reengagement of the latch. In addition, the forming of the detent pawl toothing at the rotatable part of the threaded screw drive requires fairly high expenditures with respect to the manufacturing.
The present invention relates to a further improvement of a spring brake cylinder of the above-described type such that a reliable functioning of the emergency release device is achieved in a simple manner.
The present invention relates to a spring brake cylinder having an emergency release device, particularly for rail vehicles, comprising: a housing; a spring piston which can be moved axially within the housing by one of at least one accumulator-type spring for operating a spring brake in the event of a release pressure medium drop and a spring pressure chamber for releasing the spring brake when the chamber is acted upon by a release pressure medium; a normally locked, not self-locking threaded screw drive arranged in a flux or transmission of force between the spring piston and an output-side piston rod; an outer-radial sliding surface having a detent flank, the outer-radial sliding surface being an element of a rotatable part of the threaded screw drive that rotates with respect to the housing, and the threaded screw drive having a pitch dimensioned such that the rotatable part carries out less than a complete rotation along its maximal axial adjusting stroke, and the detent flank being configured for locking the emergency release device; and a latch, held in contact with the sliding surface, for interacting in a form-locking manner with the detent flank to lock the emergency release device, and for releasing the spring brake in the absence of the release pressure medium by manually unlocking the not self-locking screw drive and thereby permitting axial movement of the spring piston.
According to the present invention, an avoidance of a plurality of teeth on a ratchet, a wearing of the toothing as a result of an unfavorable engagement situation of the latch during the movement of the rotatable part of the threaded screw drive is avoided. In the event of a brief operation as a result of a slipping off the handle of the latch, the latch always comes to rest on the sliding surface. A skipping of a tooth by the latch, which would cause damage, is made impossible in that the rotatable part of the threaded screw drive can maximally carry out not more than one complete rotation. The engaging position of the latch is therefore precisely defined. This position is exclusively located in an end position of the piston after a restoring of the operability from an emergency-released condition of the spring brake cylinder.
The sliding surface of the part of the threaded screw drive which can be rotated relative to the housing is constructed in the manner of a curved path. In this case, the detent flank constructed on the curved-path-type sliding surface preferably has an essentially radially aligned surface in order to ensure a secure engagement of the latch. The curved-path-type sliding surface has a stroke difference which occurs in an interaction with the latch and that stroke difference can be utilized for indicating a switching condition of the emergency release device. The curved-path-type sliding surface may be provided with additional shaped-on sections or indentations in order to be able to judge from an outside view of different resulting stroke differences, for example, in the emergency-released condition, the degree of release of the brake.
Within the scope of the present invention, the detent flank constructed on the sliding surface can be shaped in a groove-type manner as an indentation or in a tooth-type manner as an elevation or in another shape permitting a detent engagement with the latch.
The emergency release device according to the present invention, when used with spring brake cylinders, may be configured such that a part of the threaded screw drive rotatable relative to the housing is constructed as a screw. The screw may be axially displaceable or displaced together with the piston rod and the screw may be disposed to be rotatable about the piston rod and may interact with a nut of the threaded screw drive. The nut may be a non-rotatable part, and may be stationarily arranged with respect to the spring piston.
As an alternative the part of the threaded screw drive rotatable relative to the housing may be constructed as a nut. The nut may be axially displaceable or displaced together with the spring piston and the nut may be coaxially rotatably disposed on the spring piston, and may interact with a screw of the threaded screw drive. The screw may be a non-rotatable part and may be stationarily arranged with respect to the piston rod.
In the above case of the rotatable screw, a gear wheel element, which has an outer-radial sliding surface with the detent flank, according to the present invention, can be stationarily fastened, at an end side, to the screw as a separate component. On the whole, the manufacturing of the rotatable screw is simplified thereby and a separate exchange of a worn component can take place by demounting.
A spring arranged between the latch and the housing is preferably provided in order to hold, in the manner of a compression or tension spring, the latch in a continuous contact on the sliding surface of the rotatable part of the threaded screw drive. In addition to a manual operation, it is conceivable to operate the latch against the spring force also by means of an auxiliary device in a remote-controllable manner. As the auxiliary device, a switch-controlled electric or pneumatic actuator could be used, in which case the auxiliary energy required for this purpose may optionally be made available by storage in a battery or a pressure reservoir.